Research into displays in recent years has been stimulated by the demand for improved performance, particularly in relation to higher definition (high vision, etc) and flatter devices.
Leading the way in flat panel technology are liquid crystal displays (LCDs) and plasma display panels (PDPs). PDPs are particularly suitable for thin, large-screen applications, and 50-inch class models are already being developed.
Direct current (DC-type) and alternating current (AC-type) are the two broad categories of PDP, although AC PDPs are currently preferred for their particular suitability in large-screen applications.
FIG. 11A shows a sectional view of a main part of an exemplary prior art surface discharge AC PDP. FIG. 11B shows a sectional view along the A—A axis of the prior art PDP.
A PDP is commonly composed of a matrix of colored luminous cells. A known surface discharge AC PDP, as disclosed, for example, in unexamined patent application publication 9-35628 published in Japan, has the structure shown in FIGS. 11A and 11B. In this PDP, a front glass substrate 211 and a back glass substrate 221 are arranged parallel to and facing each other with barrier ribs 224 interposed therebetween. A parallel pair of discharge electrodes (scan electrode 212a and sustain electrode 212b) are arranged on the facing surface of front glass substrate 211, and covered with a dielectric layer 213 and a protective layer 214. An address electrode 222 is arranged on the facing surface of the back glass substrate 221 so as to extend in an orthogonal direction to electrodes 212a and 212b. Colored luminous cells are formed by arranging a colored phosphor layer 225 within a space 230 defined between the interposed barrier ribs. Space 230 is filled with a discharge gas containing neon and xenon, for example.
In this PDP, a drive circuit applies a voltage to each of the electrodes. Since each cell can only express the states of “on” or “off”, however, one field is divided into a plurality of subfields, and then by controlling the on/off timing of each subfield and thereby varying the combination of “on” subfields, intermediate graduations may be expressed with respect to the colors red (R), green (G) and blue (B).
Image display in a PDP is generally achieved in each of the subfields by using the so-called address display period separated subfield (ADS) method. This method involves a setup period, an address period, and a sustain period that are conducted consecutively. In the setup period a pulse voltage is applied uniformly to all the scan electrodes. In the address period a pulse voltage is applied sequentially to the scan electrodes as well as to address electrodes selected from among the plurality of address electrodes, and as a result wall charge is stored in the cells to be turned on. Finally, a pulse voltage is applied between the scan and sustain electrodes in the sustain period in order to sustain the discharge. Ultraviolet (UV) light is generated as a result of the sustain discharge, and image display is achieved when the phosphor elements (red, green, blue) are excited to illumination through contact with the UV light.
An object of the prior art PDP is to enhance luminous efficiency while maintaining a low drive voltage, this being a long-held objective of PDP designers. Keeping the drive voltage at a low level helps to simplify the circuitry architecture and minimize any losses relating to inefficient power usage.
In view of these factors, the pressure of the gas enclosed within the PDP is generally maintained at approximately 40 kPa to 65 kPa, and the xenon (Xe) component of the gas is maintained at around 5 vol %. Furthermore, the size of a gap dp (surface discharge gap) between the scan electrode 212a and the sustain electrode 212b in each pair is established at a value close to the minimum discharge voltage shown on a Paschen curve (generally about 80 μm), thus maintaining an external sustain voltage Vsus in a range from 180V to 200V.
As shown in FIGS. 11A and 11B, the discharge electrodes 212a and 212b are composed of transparent electrodes 2121a and 2121b and metal bus lines 2122a and 2122b, which allows for the discharge to expand by way of the transparent electrodes.
While conventional technology has been effective in enhancing the luminous efficiency of PDPs, currently achievable efficiency levels of approximately 11 m/W are still only about one-fifth of that achievable by cathode ray tube (CRT) displays.
Increasing the xenon partial pressure of the enclosed discharge gas has also proved effective in enhancing luminous efficiency. U.S. Pat. No. 5,770,921, for example, achieves this result by establishing the xenon component at 10 vol % or greater. Still further improvements are desired, however.